Minutes of ATF2 weekly meeting, 8 June, 2011

June 8 15:00 - 16:00 (JST time), Webex and ATF LC meeting room, KEK

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Recovery Status of ATF, N.Terunuma

In last week, we injected the beam on 31 May. We stored the beam with 0.2x10¹⁰/bunch in DR on 2 June and we transfered the beam to the dump without loss on 3 June.

Next, we like to increase the beam intensity for the tune-monitor system in DR, i.e. the intensity of > 1 x 10¹⁰ is needed. In this week, we re-align the DR in daytime and check out the beamline components and re-tune the beam in evening time. Today (Wednesday), we will resume the beam operation in evening.

IPBSM Status report, M.Oroku and J.Yan

First, Oroku reported present status. The seed and powered lasers were checked to be OK, i.e. there is no damage due to the earthquake. After the concrete shield work, the cables were re-connected. Some of them is not yet connected in the crowded area for difficult work where we like to improve such situation. There has been deficiency in the AC power lines at the DAQ electronics area. It is improved by adding switch boards. The VME controller was repaired by replacement of hard disk which has been broken before the earthquake, where the old software system was recovered instead of installing new system with help of KEK online group.

The recovery status of Shintake monitor (IPBSM) will be presented at TIPP11 by Y.Yamaguchi, i.e. the DAQ, gamma detector, optical system, optical monitors for the laser system to be checked while the laser and the control system are working well. There are hardware upgrades. The framework of the mirror box support will be re-inforced to suppress the laser beam fluctuation in the transport. The rack of controllers near IPBSM will be fixed to the wall for isolation of vibration from IPBSM. The laser orbit will be stabilized by mirrors fed back with PSDs. The mirrors on the concrete shield were covered by heat insulation box. We expect the laser position fluctuation at IP to decrease from 10um to 1um.

In order to improve laser profile, there are following three plans, i.e. A,B and C. The plan A is a cleaning all optical elements by hand, the B is to add a clean hut covering the Shintake optical/vertical table and the C is to install a pin-hole collimator for eliminating non-Gaussain tail of the laser pulse. The plan C will be the final one if the A and B do not have any improvement.

The gamma detector will be calibrated by cosmic ray. It takes 2 weeks. The intermediate collimator will be re-installed to shield scattered photons from the upstream of the last bending magnet. Background study with this collimator has stopped for the earthquake.

Next, Jacqueline reported the 30 degree mode commissioning status. In previous experiments, we could not switch properly to the 30 degree mode. Major reasons are identified to large jitter of the Compton signals, large spot size/bad profile of the laser at IP and the background from the last bending magnet. We expect that the 30% jitter can be reduced to 10% by the hardware upgrades. One issue in the large jitter may be a variation of the electron beam size during scans. So, we will monitor the current of QD0/QF1 for this purpose. The time needed for z-scan switching from the 8 to 30 degree mode was estimated as a function of beam size for cases w/ and w/o the upgrades. For the beam size of 300nm, 40 minutes would be reduced to 10 minutes. In addition, the beam orbit must be stable at IP. The orbit jitter should be less than 50nm for the 100nm beam size measurement, where the orbit must be measured by the IPBPMs with the position resolution of less than 30nm.

Q : Which is the bending magnet of the background (BG) source ?
A : It is the last bend in front of dump.
A : The BG were generated at the beam pipe in the bend but not the collimator. We have been testing the collimator in terms of BG from the bend when the earthquake had happened .
C : The BG is a function of betas too.
A : Position and aperture of the previous collimator were wrong, since the gamma detector was exposed to the BG.
A : The beam halo is very sensitive to the IP beta functions, too.
Q : Do you want to monitor the beam profile at IP ?
A : Yes, we suspected the beam size instability during the scans for several minutes. We want monitor the Q-currents to estimate the profile jitter.
C : The current must be precisely monitored ( by the HA-PS).
A : The beam size should be stable. We need/like to confirm it.
Q : Concerning one of the hardware upgrades, how do you expect the improvement of the laser orbit stability from 10um to 1um ?
A: We have measured the 10um fluctuation from the knife edge scan for the laser profile with reduced intensity. The stabilization with the PSD feedback has been measured. The details will be discussed by Y.Yamaguchi.
Q : How do you reduce the Compton signal jitter of 30% to less than 10% ?
A : As explained, the main one is high background, low signal intensity and the bad laser profile. They will be improved by the upgrades. The orbit, beam size jitters will be monitored.
C : Also you can change the IP beta functions as they can strongly affect the BG from the bending magnet.

Discussion on the date of TB and project meetings

According to the discussion, Terunuma-san, new ATF spokesman since this April, announced on 11 June as follows;
12th TB/SGCs joint meeting
Date & Time: July 15th (Fri), 2011, 14:00~(17:00)
Place: KEK with WebEx

The ATF2 project meeting will be held separately at KEK in this fall. Also we may have ATF2 sessions at the LCWS2011, 26-30 September, Granada as we did in Oregon. The dates will be decided for participation in person as much as possible.

Next meeting is 22nd June, 2011, since it is skipped for TIPP 2011 in this week. The ATF2 session of TIPP 2011 was held in Saturday, 11 June. The presentations can be downloaded at the homepage of http://indico.cern.ch/sessionDisplay.py?sessionId=20&confId=102998#20110611 .